The present invention generally relates to ultrasonic testing of objects and, more particularly, is concerned with a method for adjustment of transducer position to compensate for ultrasonic testing beam alignment errors.
As depicted diagrammatically in FIG. 1, a prior art ultrasonic immersion testing system 10 typically involves the use of an immersion tank 12 for holding an object 14 immersed in a coupling fluid 16 and a manipulator 18 positioned on the tank 12 such that the pointing direction 20 of the manipulator 18 intersects the object 14 at known coordinates. The manipulator 18 mounts a transducer 22 which also is immersed in the coupling fluid 16 and generates an ultrasonic beam 24 toward the object 14 to be inspected or tested.
Ultrasonic immersion testing requires that the ultrasonic beam 24 intersect a surface 14a of the test object 14 at a defined angle. For 20 most volumetric inspections, the ultrasonic beam 24 should be parallel to a normal vector 26 from the object surface 14a at the point of intersection 28 of the beam 24 with the surface 14a. However, in most ultrasonic immersion systems, small angle errors E will be present between the positions of the manipulator 18 and transducer 22 of the system 10 causing the pointing direction 20 of the manipulator 18 and the direction of the ultrasonic beam 24 from the transducer 22 to be offset or diverge from one another such that the ultrasonic beam 24 will not be parallel with the normal vector 26 at the point of intersection 28 of the ultrasonic beam 24 with the surface 14a of the object 14.
Ultrasonic immersion systems capable of scanning complex shape objects use information collected from computer-generated descriptions of the object or from "teach and learn" scanner applications to orient the transducer. These systems typically use simplified geometric algorithms to position the transducer for evaluation of the object. These systems, however, cannot correct for position and angle offsets that are associated with the transducer and the manipulator. These offsets can lead to errors in the positioning and orienting of the transducer which can reduce the detection capability of the ultrasonic evaluation.
The small errors in the transducer alignment relative to the manipulator pointing direction can lead to larger angle errors between the ultrasonic beam and the surface normal vector. The significance of the positioning errors are increased by the surface curvature of complex shape objects. Errors in the location of intersection between the ultrasonic beam and the surface of the object will lead to increased errors in the alignment of the ultrasonic beam relative to the surface normal vector at the point of incidence.
This additional alignment error limits the use of contour following methods on complex shape objects. Objects with small radii of-curvature will have larger angle alignment errors for the same beam position errors. To use contour following methods to scan complex shape objects, these positioning errors caused by misalignment of the ultrasonic beam must be minimized.
Consequently, a need exists for an innovation which will provide a solution to the aforementioned misalignment error problem without introducing any new problems in place thereof.